1. Field of the Invention
The present invention relates to an image pickup apparatus suitable for, for example, a video camera, a monitoring camera, a digital still camera, or a broadcasting camera, which uses a solid-state image pickup element,
2. Description of the Related Art
As a photographing optical system used in an image pickup apparatus including a high definition solid-state image pickup element, a zoom lens having a wide angle of field and sufficiently high optical performance has been in demand. In particular, in view of increasing image quality, an optical system having high optical performance capable of satisfactorily adapting to an image pickup element having the number of pixels ranging from Standard Definition (SD) image quality to megapixel or full High Definition (HD) image quality or more has been sought for.
As a zoom lens satisfying those demands, in each of Japanese Patent Application Laid-Open No. 2011-112909 and Japanese Patent Application Laid-open No. 2011-175174 there is disclosed a negative lead type two-unit zoom lens consisting of, in order from an object, side to an image side, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power, in which the both lens units are moved to perform zooming.
In recent years, a zoom lens used in a monitoring camera has been required to have a wide angle of field so as to be able to photograph a wide range. The zoom lens has also been required to be an optical system having a small f-number (FNO) so as to be able to capture a clear image even in night photography. In addition, in twilight and night photography, it has been required that a chromatic aberration be satisfactorily corrected in a wide wavelength range from visible light to a near-infrared region, that a defocus be small, and the like to facilitate photography under low illuminance using near-infrared light having a wavelength of 800 nm to 1,000 nm. Further, the zoom lens has been required to be small to facilitate installation in any place indoor and outdoor.
In the negative lead type two-unit zoom lens described above, in order to obtain the high optical performance over an entire zoom range while the zoom lens is small and has the wide angle of field, it becomes important to appropriately set lens configurations of the lens units. In order to obtain an image in which the chromatic aberration is satisfactorily corrected in the wide wavelength range from a visible range to a near-infrared range and the defocus is small, it becomes important to configure the optical system so that a difference in focal length of the zoom lens is small in the wide wavelength range.
The two-unit zoom lens described in Japanese Patent Application Laid-Open No. 2011-112909 is increased in relative aperture and reduced in size, but has a tendency for focus movement to increase in the near-infrared range. The two-unit zoom lens described in Japanese Patent Application Laid-Open No. 2011-175174 supports the wide wavelength range from a visible light range to a near-infrared light range and has the high optical performance supporting megapixelation, but movement amounts of the first lens unit and the second lens unit for zooming are large to increase the size of the zoom lens.